Pressure-gage



(NoM0de1.)

W. H.1VIAGGREGOR.

PRESSURE GAGE.

1 FE A 4 Sheet,sSh eet' I. I

Patented Jan. 22, 1884.

I WITNEEEEE E INk/ERI'TEIR 4' Sheena-Sheet 3.

(NOMQd61.)

I W. H. MACGREGOR.

. PRESSURE GAGE.

Patented Jan. 22, 1884.-

- I INVENTEIR g- 7 v A/ITNEEEEE' I -(No Model.) r I 4 Sheets-Sheet 4.

" W. H. MAGGREGOR.

PRESSURE GAGE.

' No. 292,169. I Patented Jan. 22, 1884..

N. PETERS. nwwumuin w. Washinginn. n.c..

UNITED STATES PAT T OFFICE.

WVILLIAllIH. MAOGREGOR, OF EAST BRAiINTBEE, ASSIGNOR TO THE ASHCROFTMANUFACTURING COMPANY, OF BOSTON, MASSACHUSETTS.

PRESSURE-GAGE.

SPECIFICATION forming part of Letters Patent N 0. 292,169 dated January22, 1884.

Application filed December 18, 1882.

To all whom it may concern.-

Be it known that I, WVILLI M H. MAoGREG- OR, of East Braintree, in thecounty of Norfolk and State of Massachusetts, a citizen of the UnitedStates, have invented a new'and useful Improvement in Pressure Gages, of

which the following is a full, clear, and exact,

description, reference being had to the accompanying drawings,forming apart of this specification in explaining its nature, in which- Figurelis a front elevation of a steam-gage manufactured by the AshcroftManufacturing Company with my improved attachment, the dial andindicator being removed. Fig. 2 is an enlarged view, representing infront elevation a portion of the same gage, the link connecting theBourdon spring, with the movement being broken off, to show theapplication of my invention to this form of gage. Fig. 3 s a verticalsection of the casing, representing in plan a portion of the gage shownin Fig. 2. Fig. 4 shows, in vertical section, a take up for means forvaryingthe tension of the spring, hereinafter described. Fig. 5 is anelevation of a gage with the dial removed, representing another methodof employing my invention.

Fig. 6 is a section upon the line 7 y of Fig. 5.

Fig. 7 is an elevation representing the use of a coiled spring. Fig. 8shows the employment of a volute spring. Fig. 9is a gage having twoBourdon springs containing my improvement. Fig. 10 shows another mode 0attaching the regulating-spring. This invention relates to that class ofpressure-gages which employ apressure-spring and it consists in theapplication of an independent co-operatin g spring at or near the freeend of the Bourdon spring.

In steam-pressure gages employing the Bourdon-tube spring the pressureof fluid within the bent flattened tube has a tendency to convert thetube from its oval to a more cylindrical form, and in so doing tostraighten 'out the curves of the spring. The twisted spring describedin the English patent to Cowper is now seldom, if ever, used, theordinary spring be ing the flattened springbent into a circular orsegmental form and it is therefore with reference to gages employingthis Bourdon spring 50 that my invention will be described. Under heavypressures, and particularly when the (No model.)

. spring is hot, it is apt to take a permanent set, the temper of thespring being drawn at such high heats. This set of the spring is notuncommon on portable engines where the steamgage is applied directly tothe outside'of the boiler, instead of to awall or post at some distancefrom the boiler, with a column of condensed water interposed between theboiler and the gage for when placed directly on the outside of theboiler the temperature of the gage is much higher than atmospherictemperature, and the temperature within the sealed case of the gage ishigher even than upon the exterior, from which heat is comparatively 6rapidly radiated into the atmosphere. This tendency to set may be inpart or in whole coun- .teracted by employing an independent springwithin the case of the gage, preferably of a different metal from thatof which the tube is formed, which shall act in aid of the tubeand'restore it to its normal position at the close of work, thusreseating the hollow spring at its initial-point before it begins toslowly cool. The position to be adopted for this spring is one involvingconsiderable care. As the free end of a Bourdon spring moves in anevolute of a peculiarcharacter, and differing in some degree for almostevery length and strength and curvature, and as the independentco-operating spring ought to be of such a character as to pull in everyposition of the end of thehollow spring, in describing its evolute, at atangent to the direction of the evolute, this would seem to be a work ofconsiderable difficulty. As, however, the motion of the free end of thehollow spring is in any instance exceedingly smallnever for the highestpressures in practice exceeding half an inch, and generally very muchless-it has been found in practice that the evolutedescribed by the freeend of the spring in actual work does not differ 'much from an arc ofcircle the radius of which does not exceed the diameter of the circle onwhich the curved hollow spring is struck, and for prac= tical purposesmay be assumed as an arc of a circle whose radius is as small as halfthe ra dius of the circle on which the springv is struck. If, therefore,the evolute described by the free end of the spring for a given pressurebe determined, and the center ofa circle of convenient radiussubstantially coincident atits ends with said evolute be formed, aradius-bar may be pivoted on this center, and also to the free end ofthe spring, without interfering with the freedom of motion of the freeend of the spring, except by the mere impediment of its weight; and if avolute, helical, or other torsional spring be placed on the centralarbor of the radius-bar to counteract the unfolding motion of the freeend of the hollow spring, a very accurate counterpoise can be effected.I have also discovered that if, in lieu of this radiusbar with a helicalspring on the pivot, or the same bar with a spring attached to the case,and acting either by compression or extension to reseat the hollowspring, I employ a leaf-spring centered at this center of motion, andfastened to the radial bar or to the end of the Bourdon spring, theresult does not substantially differ. I have also found that if a spiralspring be extended from the end of the hollow spring to some point inthe case in a line substantially tangential to the curve of the springat its terminus, the result is substantially the same if the spiralspring be of sufficiently large diametersay a quarter or three-eighthsof an inch-and the points of attachment be not made too fine, becausethe tangent of the evolute between the shortest and the longest point onpractical work will lie wholly within the helix; and because, also, bythe use of loosely fitting interlocked hook attachments to the case andto the end of the hollow spring a compensation in the direction of thepull of the spring is made. This, therefore, appears to be the bestmethod of applying the compensating-spring, which I prefer, as thesimplest and cheapest. There should be at some point in the length ofthis compensating-spring a means of adjustment, so that in case ofemergency its tension may be increased or diminished. Such a means ofadjustment would be represented by an ordinary take-up link; but perhapsastill better method, because cheaper, would be to make the hook, whichis attached to the case, to pass entirely through the case and have atake-up nut upon the outside, so that the spring could be reset at itsinitial point, if desired, and the gage re seated without opening thecase.

It is well known that the tempers of steel and brass vary differentlyaccording to temperatures, and by proper selection of material, or thetemper of this compensating or co-operating or supplemental spring theproper compensation can be made. It is also true that corrosion changesthe tension and character of the hollow spring, and this corrosioncannot well be prevented,particularly upon the interior of the hollowspring, by any method known to the arts. But it is easy to protect theexterior of this supplemental spring from corrosion either by lacqueringor plating; and by means of the take-up its power can be brought intoplay to supplement the action of the hollow spring, and so compensatefor any loss in tension from change either in the temper or structure ofthe'hollow spring.

Iain aware that small volute springs of low tension have been used onthe pinion-arbor of a gage-movement for many years; but these are onlyemployed to keep the pinion-teeth in contact with the segment gear orrack and eliminate backlash. This invention places a strong spring indirect connect-ion between the free end of the Bourdon tube and thefixed case of the gage, whereby the deterioration in strength of theBourdon spring may be compensated from time to time, and a comparativelyweak Bourdon spring made at first to show the indications of a strongerone. This auxiliary spring would never, in any case, be in the movementunless applied on the arbor or arm of the segment-gear to resist itsforward revolution, or on the connectingrod from the Bourdon tube to thesegmentgear for the same purpose.

It is obvious that instead of connecting this auxiliary spring fromBourbon tube to case of gage it will serve its co-operative purposeequally well if connected from one tube to another oppositely-curvedtube in a gage of the same type, and be within the specified invention.

Referring to the drawings, A represents a single Bourdon tube; B, thegage-casing; G,t11e link connecting the free end of the Bourdon tubewith the gage-action; D, the auxiliary or supplemental spring,which inthis instance is attached to the free end of the Bourdon tube and to thecasing of the gage. E'represents a hook, to which the spring D may befastened, and which is capable of being moved or adjusted in relation tothe casing of the gage by means of the screw-sleeve F, the sleeve beingsecured to the casing so that it can be revolved, and having ascrew-thread which engages with a screw-thread upon the shank of thehook. If desired, the sleeve can extend through the casing of the gage,so that an adjustment of the spring D may be made from the outside.

In Fig. 5 I show my regulating or adjusting spring attached to thecasing of the gage and to the end of the lever G. This lever is pivotedat g to afulcrum,which maybe movable, if desired, and it is connectedwith the free end of the Bourdon spring by means of the link 9'. In Fig.6, I show in section a fulcrum-post, g, movable in ways 9 and thefulcrum is movable in the slot 9" in the lever. The fulcrumpost islocked in any desired position bymeans of a nut. By changing the fulcrumof course the amount of stress or resistance upon the end of the Bourdonspring is varied. In Fig. 7 I represent a spiral spring, H,which isattached at its lower end to a post, h, fastened to the casing of thegage. Its free end is secured to the free end of the Bourdon spring. InFig. 8, I represent a volute spring, M, the free end of which isfastened to the free end of the Bourdon spring. In Fig. 9 I show a gagehaving two Bourdon springs,which are connected together by means of myregulating or auxiliary spring, as represented. In Fig. 10, I show theauxiliary or regulating spring as operating upon a Bourdon springthrough the segment 1 N andlink 0, this spring being attached at one endto the casing of the gage or other proper place of fastening, and at theother to the segment. These modifications in Figs. 5, 7, 8,9, and 10only represent a few of the many Ways for applying my invention to getthe results desired, and it is obvious that there are many other modesof attaching a spring to the free end of the Bourdon spring to obtainthe result desired, and that a great many other forms of springs can beused for the purpose.

I am aware of the Patents N 0. 126,247, of

1872, to Ashcroft, No. 148,67 3, of 1874, to Oros-.

by, for registering-gages, and of the use of Weak and long-range take-upsprings on the registering-movement; but this is not my invention, whichrequires a constant tension of ashort range and comparatively strongspring directly applied without regard to a registering attachment.

I am also aware of the Patent No. 42,873, of V 1864, to Bay, which hasan adjustable take-up to the backlash-spring; but this, again, does notembody my invention,which is defined in the followingclairns.

Having thus fully described my invention, I

claim and desire to secure by Letters Patent of the'United States 1. Ina steam or pressure ,gage, the combination of a Bourdon tube with ashort-range preponderating direct-action spring attached to the free endof the said tube, and adapted to resist by its tension the movement ofthe free end thereof, and thereby weighing the pressure therein, allsubstantially-as described.

' 2. In a steam or pressure-gage, the combination of aBourdon tube,ashort-range directacting spring attached to the free end of said tube,of sufficient strength to counteract its tendency to set under pressure,all substan tially as described.

WILLIAM H. MAOGREGOR.

. WVitnesses:

F. F. RAYMOND, 2d, .WILLARD O. FOGG.

